This invention relates to the field of chemical mechanical polishing systems for semiconductor wafers of the type used in the fabrication of integrated circuits.
Integrated circuits are conventionally fabricated from semiconductor wafers, each containing an array of individual integrated circuit dies. It is important at various processing stages that the wafer be polished to a planar configuration. The present invention represents a new approach to the problem of such polishing.
Breivogel U.S. Pat. No. 5,212,910 discusses the problem of achieving local planarity at the integrated circuit die scale in a wafer that itself is to some extent curved. The Breivogel patent discloses a composite polishing pad that includes a base layer of a relatively soft elastic material, an intermediate rigid layer, and a top polishing pad layer. The intermediate rigid layer is segmented to form individual tiles, each having a size comparable to that of an integrated circuit die. In use, individual tiles press into the first resilient base layer as necessary to allow the respective polishing pad to conform to the non-planar wafer.
With this approach the individual tiles are not completely isolated from one another, because the resilient base layer extends between the tiles. Furthermore, the resilient base layer is designed to allow individual tiles to move in the Z direction, away from the wafer being polished. This approach may place unusual requirements on the polishing pad material.
The present invention is directed to a new approach which, to a large extent, overcomes the problems discussed above.